1. Field of the Invention
This invention relates to molding devices, and particularly to an apparatus for molding two unjoined items during a single molding process in a single mold cavity.
2. Description of the Art
Rotational molding systems are well know. For example, U.S. Pat. No. 5,306,564 describes a mold wherein two metallic (aluminum) molding portions are brought together to form a mold cavity in which a single molded item is cast.
To form an item using such a mold, molding particulate (usually a plastic such as polyethylene) is placed inside the cavity, the mold is closed, the mold is placed in a furnace where it is heated (or is otherwise heated), and the mold is rotated. The particulate melts and sticks to the internal surface of the is cavity. After a plurality of rotations, the entire internal surface of the mold is coated with the melted particulate. After cooling the mold is opened and the molded item is removed.
Unfortunately, melted plastic often seeps into the seam between the mold halves. As a result, there is an imperfectly formed article. This excess material is usually trimmed from the final product and discarded after the molding process. Trimming is labor intensive and can be wasteful. Also, the presence of such material can sometimes make it more difficult to open the mold.
Moreover, if multiple items are desired from a single casting, the molded item must be cut in two (usually along the seam line formed at the sealing edges of the two mold halves). This requires a cutting step and a cutting system, and can impose limitations on the shape of the items being formed.
It would therefore be advantageous to have a rotational mold that inhibits material from leaking out of a mold seam and permits two unjoined items to be directly formed in the mold cavity.